There are many environments in which it is not possible or convenient to position a fixed light source where it can illuminate a fixed object. This is particularly a problem with human powered vehicles such as bicycles where weight, cost, and wind resistance are major concerns. Bicycles frequently have accessory devices such as speedometers or computers attached to the handlebar where they can be safely observed by the rider. At night these devices cannot be used unless they are illuminated. A fiberoptic light guide positioned to receive light from the bicycle's headlight and illuminate an area near the handlebar would allow use of such devices at night without significantly increasing weight or wind resistance. The light guide must be flexible enough to operatively position its ends to receive light from the headlight and transmit it to the handlebar. The light guide must also be able to retain its shape after being so positioned. Conventional fiberoptic cables or devices are either too flexible or too stiff for this purpose and are not typically designed to retain a variable flexed shape.
Optical cables having elongated reinforcing members are well known. U.S. Pat. Nos. 4,141,622 to Beal and 4,153,332 to Longoni disclose optical cables having central reinforcing members made of steel wire. U.S. Pat. No. 4,141,622 to Beal also discloses a plurality of plastic elongate members interspersed with optical fibers of equal diameter to provide additional tensile reinforcement. U.S. Pat. No. 4,420,220 to Dean et al. discloses a pair of steel wire reinforcing members located on either side of the optical fibers. The purpose of these reinforcing members is to protect the optical fibers from tensile stress while maintaining flexibility. An optical cable is typically designed to be wound on drums or spools for storage and shape retention is not a desirable characteristic.
Optical cables which have been treated to maintain a fixed shape are also known. U.S. Pat. Nos. 3,817,595 to Edelman et al. and 4,852,964 to Holland et al. disclose helically coiled cables in which the optical fibers are contained within a jacket made of a material having a plastic memory. The cables are curled on a mandrel and then heat treated to set the shape of the sheath. These cables can accommodate a variety of separation distances between their ends but they are unable to retain a manually formed variable shape.
Optical devices for illuminating remote objects from a fixed light source are also known. U.S. Pat. No. 5,109,461 to Churchill discloses a fiberoptic light device for use in illuminating an object being examined with an optical comparator. The device has a hollow U-shaped housing with a pair of flexible segmented conduits containing optical fibers located on opposite sides of the U. Each conduit contains a separate bundle of fibers which are mechanically fixed to one another along their length by a UV-cured adhesive. The conduits extend inwardly from mounting collars on the outer surface of a metal cover plate and are adjustably positionable for illuminating the object. Shape retention is provided by the external conduit. U.S. Pat. No. 5,086,378 to Prince discloses a fiberoptic finger light for use with night vision devices in an aircraft cockpit. The light source is strapped to the wrist of the operator and connected to a pair of fiberoptic cables which are strapped to the operator's finger.
Incorporation of a deformable elongated member into a structure in order to provide shape retention is also known. U.S. Pat. No. 4,966,741 to Rush et al. discloses a shape retention hose construction where a deformable elongated member is located on the outer surface of a hose in a projecting channel.
Prior art optical fiber cables and devices are not designed to retain a variable flexed shape. Bending of an optical fiber cable into a convoluted shape necessitates longitudinal motion of the individual fibers relative to one another and to the cable jacket. Prior art devices in which the optical fibers are mechanically fixed to one another at both ends or along their length cannot be bent into convoluted shapes. Fixed light sources and objects to be illuminated are often located in variable positions relative to one another and a fiberoptic light guide must accommodate a variety of separation distances. Prior art devices which can accommodate a variety of separation distances are not designed to be manually deformed and retain a variable flexed shape.
It is therefore an object of the present invention to provide an improved fiberoptic light guide capable of retaining the shape to which it is manually formed.
It is a further object to provide an improved light guide which can be bent into convoluted shapes.
It is a further object to provide an improved light guide which can be adapted to accommodate a variety of separation distances, relative locations and intervening environments between light source and illuminated object.